Apparatus for measuring charge condition within a solution



W. F. GERDES APPARATUS FOR MEASURING CHARGE Feb. 6, 1968 CONDITIONWITHIN A SOLUTION Filed March 4, 1966 a J a 2 5 .H 4 v W5 Q 7 1% m. M.w'lll m 5 5mm Z 6 w w 8 o 7 M E WU W Z 44 w Wm M 0 2 1 z z 1/ I/K 7 y mKMEKQMQK n KQ \M AME rig.

' INVENTOR. W0//er' F Gare/es ZZAM United States Patent Ofi 3,358,145Patented Feb. 6, 1968 3 368,145 APPARATUS FOR MEASURING CHARGE CONDITIONWITHIN A SOLUTION Walter F. Gerdcs, Lake Jackson, Tex., assignor to TheDow Chemical Company, Midland, Mich., a corporation of DelawareContinuation-impart of application Ser. No. 315,537,

Oct. 11, 15 63. This application Mar. 4, 1966, Ser.

11 Claims. (6]. 32432) This application is a continuation-in-part of mycopending application Ser. No. 315,537, filed Oct. 11, 1963, for ControlApparatus, now abandoned.

This invention relates to novel apparatus for developing an alternatingcurrent electrical signal which can be utilized in the continuousregulation of flocculation of aqueous suspensions of finely dividedcharged particles and for other uses.

It is conventional practice in clarifying aqueous systems containingsuspended particles to employ a flocculation operation. Onceflocculated, the suspended particles can be separated from their watermedium by sedimentahon, filtration, flotation, centrifugation, or one ormore of the foregoing physical separatory processes in combination.Conventionally the flocculation operation is promoted by the use offlocculating chemicals such as alum, ferric chloride and variouspolymeric materials such as water-soluble cationic and anionic organicpolyelectrolytes. Aqueous suspensions of finely divided particles areencountered in natural or raw water supplies such as rivers and lakesand in municipal and industrial wastes, which latter systems include asubstantial proportion of suspended organic particles.

In a typical flocculation process for the clarification of municipalsewage, a Water-soluble cationic flocculating chemical is added to thesewage. The sewage normally comprises suspended negatively chargedorganic particles and thus the addition of the cationic agent results incharge neutralization on the suspended particles. When the averagecharge is zero, or some other predetermined value, the dispersed organicparticles undergo flocculation, i.e., aggregation, at an optimum rate.Too much cationic agent, however, creates positively charged organicparticles which can be as difficult to fiocculate as are the originallynegatively charged particles.

To date, however, determining how much chemical to add to the stream tobe treated has been difficult, especially since the composition of suchstreams often varies over fairly wide ranges in time intervals of a fewminutes to a few hours.

Various empirical approaches to finding the correct dosage of fiocculantto be added to a stream have been used. For example, increasing amountsof flocculant may be added to samples from the stream and the amount ofdecrease in turbidity of the stream noted, the correct dosage beingdetermined as the one which causes the greatest decrease in turbiditywith the least addition of fiocculant. Such a procedure is timeconsuming and therefore not really suitable where the composition of thetreated stream varies.

Another approach is to use a so-called Zeta meter to determine thecharge condition existing in the stream. The Zeta meter is used toobserve the time required for a charged particle from the stream to passa predetermined disance along a liquid path while under the influence ofan electric field. This method is time consuming and requires atechnician to perform the test and to interpret test results before thestream is treated with a greater, lesser, or the same amount offlocculant as had been used since the last previous Zeta meter test wasmade.

The usual methods of determining the dosage of flocculant to be added toa stream having suspended charged particles are discontinuous andrequire a substantial amount of individual labor in making the tests.The use of such tests in controlling flocculation of such streams iscostly both from the standpoint of the labor involved and from the factthat the amount of flocculant actually required by the stream may varyfrom that indicated by the tests.

Accordingly, a principal object of this invention is to provide animproved instrument which is useful in controlling the dosage ofchemicals to be added to a controllable stream having a chargedcondition existing therein.

Another object of this invention is to provide an improved, simpler,instrument for use in metering the addition of flocculant to a streamhaving dispersed charged particles therein.

A further object of this invention is to provide an improved instrumentwhich is capable of developing, on a continuous basis, an electricalsignal which is a function of the charge condition existing in a streamcontaining charged particles therein.

Still another object of this invention is to provide an improvedinstrument which is capable of developing an alternating currentelectrical signal which is a function of the charge condition existingin a sample comprising liquid, the instrument being capable of operationfor substantial lengths of time without adjustment. by a technician. Anancillary object of this invention is to provide an improved means fordetermination of the end point of a titration of materials having chargeinfluencing characteristics.

In accordance with this invention there is provided a sample receivingelectrically insulating block having a sample reservoir therein andhaving a bore extending downwardly from the lower part of the reservoir.A pair of reversible electrodes are disposed within the block, one ofsaid electrodes being at least near to the lower end of the borementioned above and the other electrode being disposed near the upperend of said bore. A reciprocating rod-like piston or plunger is disposedin close fitting but slidable relationship within the bore.

Signal amplifying and signal utilization means are coupled to the abovementioned electrodes.

As sample is fed into the reservoir it enters the bore in which therod-like piston is disposed (on the upstroke of the piston) and isexpelled from the bore on the downstroke of the piston. The movement ofthe sample, which is at least predominantly liquid, into and out of thebore causes an alternating current signal to be developed across theelectrodes. The signal is then amplified and coupled to a meter,recorder, servo control device, or other utilization device. Thedeveloped signal is a function of the charge condition existing in thestream.

The invention, as well as additional objects and advantages thereof,will best be understood when the following detailed description is readin connection with the accompanying drawings, in which:

FIG. 1 is a diagrammatic view of an instrument made in accordance withthis invention;

FIG. 2 is a sectional view taken along the line 22 of FIG. 1;

FIG. 3 is a side elevational View of the upper part of the apparatusshown in FIG. 1; and

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 1.

Referring to the drawing, there is shown apparatus in accordance withthis invention for detecting the average electrical charge density onthe insulating surfaces of an annulus, the charge density being afunction of the charge influencing species, such as ions, chargedmolecules, oncolloidal particles, for example, which are present in aliquid stream in flowing contact with said surface.

The apparatus, indicated generally by the numeral 16, comprises a samplereceiving block or flow path member, indicated generally by the numeral12, which has a generally perpendicularly disposed cylindrical operatingbore 14 therein, the bore 14- extending to near the bottom of the block12. A large diameter sample receiving counter bore 16 extends from thetop 18 of the block about halfway to the lower end 20 of the block. Abore 22 extends from a side 24 of the block 12 to the counter bore 16. AT-shaped tubular element 26 is coupled to the bore 22 with thelongitudinal axis of the cross-membered part of the T beingperpendicular to the base end 26 of the block 12. A small bore 28extends from an outer surface of the block 12 and communicates with thebottom 30 of the bore 14. The bore 28 has an electrode element 32extending therethrough, its exposed end part being in the cylinder 14 ator near the bottom 30 thereof. The electrode element 32 fits tightly oris sealed in the bore 28 to prevent loss of liquid from the cylinder orhere 14 during operation of the device.

A similar small bore 34 extends from an outer surface of the block 12and communicates with, or near to, the bottom 36 of the counter bore 16.An electrode element 38, similar to the electrode element 32, extendsthrough the bore 34 and is disposed adjacent to the periphery of thebore 14, the radius of curvature of the end of the electrode element 38being at least slightly greater than the radius of the bore 14.

The crosshead guide block 40 is disposed above the block 12. Both theblock 12 and crosshead guide block 40 are conveniently secured to acommon plate member 42. The crosshead guide block 40 has a bore 44-there-in which is aligned with the axis of the bore 14.

crosshead 46 having a wrist pin coupling at its upper end '48 extendsthrough the bore 44 in the crosshead guide block 40. A piston element 50having longitudinally extending lands 52 (see FIG. 4, especially) isrigidly coupled to the lower end 54 of the crosshead 46 and extends intothe bore 14. The diameter of the piston, including the diametricallyopposite lands, is such that the piston and lands fit closely butslidably, .005 clearance, for example, within the smooth walled cylinderor bore 14.

In one instrument made in accordance with this invention the diameter ofthe bore 14 is /2 inch, the depth of the bore is 1 inch, the piston 50having a /4 inch stroke. The piston is disposed within the bore 14 aboutinch when the piston is in the upstroke position. Thus, on thedownstroke the piston 50 reaches at least very near to the bottom of thebore 14.

An electric motor 56 is secured to the base member 42 with its rotatableshaft 58 extending through the base plate member 42 (through the bore64). The shaft 58 is perpendicular with respect to the longitudinal axisof the bore 14 and crosshead bore 44, but intersects the commonlongitudinal axis of those bores. A cam 60 is coupled to the shaft 58 atleast approximately at the intersection of the shaft with the abovementioned longitudinal axis. A connecting rod 62 is coupled between thecam 60 and the upper end 48 of the crosshead 46.

A circular plate-like element 66, composed substantially of twosemi-circular sections 66a, 66b joined together along their diameters toform a single disc, is coupled to the shaft 58 at a position spaced fromthe cam 60. One half 6612 of the disc element 66 is composed of amagnetic material such as a common steel and the other half 66a of thedisc element 66 is composed of a non-magnetic element, such as brass,for example. The element 66 is coupled to the shaft 58 through thecenter of the disc with the plane faces of the disc 66 being disposedperpendicular to the longitudinal axis of the shaft 58.

The electrode 32 is coupled by means of the central lead 76 of a coaxialcable through a capacitor 78 (8 microfarads capacity is satisfactory) toone input terminal 80 of a high gain operational amplifier 82 which hassufiicient feedback, by means of the resistor 84 and capacitor 86coupled between its output and input circuits, to function as amilli-microarnmeter when a suitable utilization device such as a meteror recorder 88 is coupled to its output. The outer or shield conductor90 of the coaxial cable is connected between the upper electrode 38 andthe grounded input terminal 92 of the operational amplifier 82.

The output of the operational amplifier 32 is coupled across the primarywinding of a transformer 94. The secondary 96 has its center tapgrounded and its end leads coupled to the throws 98, 106 of amagnetically controlled single pole double throw switch 102. The switch162 is physically located adjacent to one side of the plate-like element66, while a permanent magnet 164 is disposed adjacent to the oppositeside of the plate-like element 66. The center pole 106 of the switch 102is connected, through the lead 108, to a series connected resistor 110and capacitor 112. The other electrode of the capacitor 112 is connectedto ground (as is the center tapped secondary winding 96). Theutilization device 88 is coupled across the capacitor 112.

In operation, with the motor 56 energized by a suitable source, such asa battery 68 through the switch 70, the shaft 58 rotates both the cam 68and the disc element 66.

The rotation of the cam causes the connecting rod 62 to reciprocate,thus moving the crosshead 46 and piston 50 back and forth in a cyclicmanner.

Assuming that sample material to be analyzed (have its chargecharacteristics determined) is fed into the counter bore or samplereservoir 16, the sample liquid enters the bore 14 containing thepiston. The offset of the cam 60 is such that on its downward stroke thepiston 50 comes near to but does not touch the electrode 32 which liesat the bottom 36 of the bore 14. As the slotted piston 50 reciprocatesin the bore 14 sample liquid is alternately forced into (under somedegree of vacuum) and forced (under pressure) out of the bore 14, thusflowing first in one direction and then in another between theelectrodes 32, 38.

The electrodes 32, 38 may, for example, conveniently be reversiblesilver-silver chloride electrodes.

Because the lead 76 is coupled to the input of the operational amplifier(which operates as a micro-milliammeter) in series with the capacitor78, any direct current component of the signal developed between theelectrodes 32, 38 is blocked and only the alternating signal produced bythe sample material pulsing back and forth between the electrodes 32, 38is fed into the operational amplifier 82. It should be noted, however,that it may be advantageous in the case of samples of high conductivityto connect the feedback resistor 84 to the electrode directly as shownby the dotted line 85 rather than through the capacitor 78. This lowersthe effective impedance of the measuring circuit and improves theeffectiveness of collecting and measuring the generated current. This istrue because the deleterious effects of the capacitor are in proportionto the current flowing through it and in the latter circuit this currentis reduced by a factor of 15 or 20.

The output of the operational amplifier 82 is couppled across theprimary winding of the transformer 24, as mentioned previously. Becauseit is desirable to couple the output signal to a direct current readoutdevice such as a meter or recorder, for example, the magneticallyactuated switch 102 is adapted to achieve full Wave rectification of thetransformer output appearing across the secondary Winding 96.Rectification is accomplished by connecting the center pole 106 of theswitch 102 alternately to each throw of the switch 162 in synchronismwith the pulsing of sample material by the piston 56.

The cam plate-like member 66, which is made of two semi-circularsections joined along their diameters, one of the sections 66b beingmade of a magnetic material and the other section 66a being made of anon-magnetic material, rotates between the magnetically actuated switch102 and a permanent magnet 104 disposed adjacent to but on the oppositeside of the member 66 from the switch 102. During the half revolutionwhen the magnetic part 66b of the member 66 shields the switch 182 fromthe field of the magnet 104, the switch 102 is coupled to one throw dueto the slight tension caused by the spring 114, for example. Then, whenthe member 66 rotates to a position whereby the magnetic field mayinfluence the switch 102, the pole of the switch connected to theopposite side of the secondary winding is connected to the other throwof the switch. Thus, since rotation of the shaft 58 (and member 66,attached thereto) controls both the rate (about 4 cycles per second, forexample) at which the piston 50 reciprocates and the rate at which thesecondary winding 96 output is switched, synchronous full waverectification of the output of the operational amplifier 60 is easilyaccomplished.

The resistor 110 and capacitor 112 constitute a brute force filter tosmooth the rectified output before it is coupled to the DC. actuatedutilization device or recorder 88.

It should be emphasized that the operational amplifier type ofmilli-microammeter circuit may be replaced by other apparatus, such asan electrometer, which will give considerably different instrumentcharacteristics. If the readout device gives an indication proportionalto the voltage appearing at the electrodes rather than to the current,the effects of salts orf other ionized materials in the sample will beaccentuated.

The synchronous rectification afforded by the magnetically actuatedswitch 102 results in a direct current output signal which is phasesensitive. Other phase sensitive rectifying devices, such as a ringdemodulator, for example, may be substituted for the synchronousrectifier. If it is not required to know the polarity of the electricalsignal which is measured, a non-synchronous type of rectification meansmay be used.

It has been found that best results are obtained with instruments madein accordance with this invention when no cavitation of the sampleoccurs as the piston 50 reciprocates. Also, the sample should be keptfree of abrasive and fibrous material if the tolerances between thepiston 50 and the bore 14 are to be maintained.

Using this instrument as a current measuring instrument makes the signalrelatively less dependent on the ionic conductivity of the sample streamthan is the case when the instrument is adapted to measure the potentialdeveloped across the electrodes 32, 38. F or example, when theinstrument is adapted to read current, readings of the instrument arenot adversely affected enough to become unreliable until theconductivity of the sample stream approaches the conductivity of apercent sodium chloride water solution, especially when the feedback isdirectly connected to the electrode. The instrument may readily beadapted to read the developed potential by inserting a resistance ofsuitably high value (at least several megohms, usually) in series withthe capacitor 78 and the input of the operational amplifier 82.

An an example of the amplitude of signals obtained with one instrumentin accordance with this invention, tap water (Freeport, Tex. area) areused as the sample stream developed signals of the order of lO- volt and10 ampere. However, because the capacitor 78 isolates any noise signalresulting from dis-symmetry of the electrodes 32, 38 or drift signals,the small signals developed across the electrodes 32, 38 by the movementof the sample through the bore 14 may readily be amplified.

When the instrument is to be calibrated, a standard sample from a source(not shown) is fed into the sample receiving bore 18 in the same manneras is the regular sample. After the instrument has been operated withstandard sample in the operating bore 14 for a short time, the signaltends to stabilize at a set value which is a point at which the metercan be calibrated to show the value and polarity of the charge in thesample.

The standard sample may, for example, be a colloidal solution ordispersion wherein the average charge on the particles has previouslybeen determined by other means, such as a by a Zeta meter, for example,which measures electrophoretic mobility of charged particles. Ifcalibration over a wide range is desired, the use of various standardsamples may be used.

The walls of the bore 14 may be made of glass or other ceramics,polyethylene, polystyrene, nylon, beeswax, paraffin, orpolytetrafluoroethylene, for example, or of other electricallyinsulating material having suitable dielectric characteristics. Oneblock 12 which has been used is composed of polyethylene, for example.

The outer surface of the piston member 59 may be made of glass or otherceramic material, polyethylene, polystyrene, nylon,polytetrafluoroethylene, or other electrically insulating materialhaving suitable dielectric characteristics. Usually the entire pistonrod, rather than just the outer surface of the rod, is made of theinsulating material.

The apparatus heretofore described may be used to indicate the averagecharge density existing on the material adsorbed on the wall of thepiston Sit and bore 14 from the sample stream based either on thecurrent or potential developed between the electrodes 32, 38. Typicalsample streams may be raw water, sewage, a latex, or oil-wateremulsions, for example.

This instrument provides a continuous measurement of the charge densityof the adsorbed material taken from the process stream, for example.

In applications where it is desired to produce flocculation of theparticles in the stream, the instrument is used to provide an indicationof the end point of a titration operation in which a fiuocculantmaterial such as alum, ferric chloride, or a suitable polymer such aspolyethylenimine, for example, is added to the sample stream as thecharge on the material adsorbed from the sample stream is being measuredby the instrument of this invention.

In batch titration operation, a predetermined amount of a cationictreating material to be analyzed, such as polyethylenimine, for example,is dispensed into the reservoir bore 16 in a batch'type operation. Then,with the instrument in operation, discrete amounts of a known standardanionic reagent, such as alkylbenzene sulfonate, are dispensed into thereservoir bore 16.. The amount of anionic reagent required to neutralizethe cationic material, as indicated by zero output on the instrument, isrecorded. The strength of the cationic material is then conventionallycalculated by multiplying the known strength of the anionic material bythe volume of the anionic material dispensed into the reservoir 16 anddividing by the volume of the cationic material dispensed into thereservoir 16.

When titrating materials have charge influencing characteristics, aninstrument reading of zero is not always obtained at the equivalencepoint because of 'diiferences in the aggressiveness of the material.Since, in general, the exact deviation of the equivalence point fromzero reading to be expected when titratin g one material with anotherWill be unknown, the trick of making a second titration right after afirst titration is very useful in titrating charge with this instrument.First, an aliquot of sample is titrated to the neutral point of zeromicroamps as indicated by the instrument. 'Then a second aliquot of thesame sample is added to the neutral mixture and the composite istitrated. The first titration is ignored and the sec and is taken as thetrue titer of the sample.

The procedure described above is useful in quality control operations,for example, in which different batches of product must be compared todetermine their relative effectiveness, as in the case of cationicfiocculants, for example.

In the illustrated embodiment of the invention the 7 lands 52 of thepiston 50, as mentioned previously, fit closely but slidably within thebore 14. The walls of the piston element St) lying between the lands 52are undercut .003 to .005 of an inch. In some instances a looselyfitting piston having no lands is used.

In addition, increasing or decreasing the clearance between the pistonand bore walls may be desirable, depending on the nature of the samplebeing supplied to the instrument.

The signals developed between the electrodes 32-, 38 are believed to bea function of the streaming current. The streaming current in turn is afunction of the constant parameters of the apparatus and charge densityexisting on the walls as a result of the sample characteristics.

What is claimed is:

1. An apparatus for determining a function of the charge condition whichis present in a system which includes liquid which contains chargeinfluencing species, comprising a tubular flow path member, said flowpath member having electrically insulating walls an open end and aclosed end, said fiow path member being so disposed that it may besubstantially filled with said liquid, a pair of electrodes, one of theelectrodes being at least near to the closed end of said flow pathmember and the other electrode being at least near to the open end ofsaid flow path member, both the electrodes being disposed so as to becontacted by said liquid entering or leaving said flow path member,means for flowing said liquid to and fro in said flow path member in acontinuing repetitive manner, means coupled to said electrodes foramplifying any electrical signals induced across said electrodes, andmeans for utilizing said amplified signals.

2. Apparatus for determining a function of the charge condition which ispresent in flowable material comprising liquid and charge influencingspecies, comprising a cuplike flow path member having electricallyinsulating Walls, an open end and a closed end, a block-likereciprocating element whose outer wall is electrically insulatingdisposed in slidable relationship within said flow path memher, saidfiow path member being so disposed that it may be substantially filledwith said fiowable material, a pair of electrodes, one of the electrodesbeing at least near to the closed end of said flow path member and theother electrode being at least near to the open end of said fio'w pathmember, both of the electrodes being disposed so as to be contacted bysaid fiowable material entering or leaving said flow path member, saidreciprocating element having a transverse cross-sectional configurationsuch that said reciprocating element fits adjacent to but spaced fromsaid electrically insulating walls of said fiow path member,

means for reciprocating said reciprocating element in said flow pathmember, means for admitting predetermined amounts of fiowable materialto said flow path member, means coupled to said electrodes foramplifying any electrical signals induced across said electrodes, andmeans for utilizing said amplified signals.

3. Apparatus in accordance with claim 2, wherein said reciprocatingelement has lands extending along its length.

4. Apparatus in accordance with claim 2, wherein said means forreciprocating said reciprocating element includes a rotating memberhaving an offset throw element coupled thereto.

5. Apparatus in accordance with claim 2, wherein the length of saidreciprocating element is at least as long as the spacing between saidelectrodes.

6. Apparatus in accordance with claim 2, wherein said means forutilizing said amplified signals includes a rectifier circuit and adirect current readout device.

7. Apparatus in accordance with claim 6, wherein said rectifier circuitis a phase sensitive rectifier circuit.

8. Apparatus in accordance with claim 2, wherein said means foradmitting fiowable material to said flow path includes a reservoircommunicating with said flow path member.

9. Apparatus in accordance with claim 2, wherein said means coupled tosaid electrodes for amplifying any electrical signals includes leads,said leads having a capacitor coupled in series with at least one ofthem.

10. Apparatus in accordance with claim 7, wherein said phase sensitiverectifier circuit comprises a magnetically actuate-d switch, anactuating magnet, said actuating magnet being spaced from said switch,and means for repetitively isolating the field of said actuating magnetfrom said switch.

11. Apparatus in accordance with claim 10, wherein said means forrepetitively isolating the field of said actuating magnet comprises arotating element of magnetic material, said element of magnetic materialbeing rotated in synchronism with the reciprocation of saidreciprocating element.

References Cited UNITED STATES PATENTS 2,769,929 11/1956 Hardway 324-71RUDOLPH V. ROLINEC, Primary Examiner.

WALTER L. CARLSON, Examiner.

C. F. ROBERTS, Assistant Examiner.

1. AN APPARATUS FOR DETERMING A FUNCTION OF THE CHARGE CONDITION WHICHIS PRESENT IN A SYSTEM WHICH INCLUDES LIQUID WHICH CONTAINS CHARGEINFLUENCING SPECIES, COMPRISING A TUBULAR FLOW PATH MEMBER, SAID FLOWPATH MEMBER HAVING ELECTRICALLY INSULATING WALLS AN OPEN END AND ACLOSED END, SAID FLOW PATH MEMBER BEING SO DISPOSED THAT IT MAY BESUBSTANTIALLY FILLED WITH SAID LIQUID, A PAIR OF ELECTRODES, ONE OF THEELECTRODES BEING AT LEAST NEAR TO THE CLOSED END OF SAID FLOW PATHMEMBER AND THE OTHER ELECTRODE BEING AT LEAST NEAR TO THE OPEN END OFSAID FLOW PATH MEMBER, BOTH THE ELECTRODES BEING DISPOSED SO AS TO BECONTACTED BY SAID LIQUID ENTERING OR LEAVING SAID FLOW PATH MEMBER,MEANS FOR FLOWING SAID LIQUID TO AND FRO IN SAID FLOW PATH MEMBER IN ACONTINUING REPETITIVE MANNER, MEANS COUPLED TO SAID ELECTRODES FORAMPLIFYING ANY ELECTRICAL SIGNALS INDUCED ACROSS SAID ELECTRODES, ANDMEANS FOR UTILIZING SAID AMPLIFIED SIGNALS.